1. Field of the Invention
The present invention relates to a method of manufacturing a molded wooden product by hot compression molding a ligneous molding material which is composed of wooden fibers with a binder consisting of a synthetic resin, etc. added thereto and which has been supplied to a mold.
2. Description of the Prior Art
Since such molded wooden products are lighter than plywoods, have high heat resistance, water resistance and moisture resistance, and are strong for their thickness, they have found extensive utility as what is called a hardboard in applications including interior materials used in buildings, articles of furniture, interior materials used in automobiles, and cabinets for television and stereo sets.
Heretofore, such molded wooden products have generally been manufactured by the following procedure. Wood chips are digested with steam and disintegrated. A binder such as a phenol resin, hemp fibers, a water-repelling agent such as rosin and paraffin, etc. are mixed with the thus-obtained wooden fibers. These wood fibers are formed into a stack of an appropriate thickness, and then lightly hot compression molded into what is called a molding mat (10 to 40 mm in thickness) with, for example, a roll press, and the mat is appropriately cut to be supplied to a shaping mold, where the mat is hot compression molded into a predetermined configuration.
The above-described manufacturing method, however, is disadvantageous in that since it necessitates the step of forming a molding material into a mat (hereinunder referred to as "mat-making"), the procedure becomes complicated, thereby making it difficult to enhance the productivity as expected, and in that since the step of cutting the mat into an appropriate size for a shaping mold is essential, the yield is lowered by that degree, thereby raising the manufacturing cost as a whole.
In addition, if a large plate body having a deeply drawn portion is formed from a single mat, the corner portions become thin-walled because it is difficult for the mat material (wood fibers) to flow into the deeply drawn portion, often resulting in production of a large cavity or a crack. As a countermeasure, the amount of hemp fibers used may be increased. In this case, however, it is necessary to add an extra amount of synthetic resin, which leads to a an in the raw material cost and, hence, rise increase in the cost of the product.
To solve the above-described problems caused by the use of a mat for molding, the present inventors proposed a method of manufacturing a molded wooden product by hot compression molding a ligneous molding material which has been supplied into a shaping mold after being aggregated into a predetermined configuration (Japanese Patent Laid-Open No. 90203/1987) or which has been supplied directly to a shaping mold in the form of fibers (Japanese Patent Laid-Open No. 259372/1985). These methods have almost solved the above-described problems resulting from the use of a mat for molding, but they involve a risk of producing a deviation of the shape of the outer periphery when a ligneous molding material is supplied into a shaping mold, so that a molded product must be formed so as to have a slightly larger configuration than the desired configuration depending upon the desired quality, and the external shape must be finally blanked, thereby disadvantageously increasing the number of manufacturing steps and, hence, lowering the yield. Furthermore, according to the above-described methods, since the bulk specific gravity of a molding material varies in accordance with the variation in the water content in the material chips, the disintegrating conditions of the chips, the dispersing conditions of a binder, etc., these methods also involve a risk of producing a surface blister due to the increase in generated gas or lack of air permeability, or a risk of producing lack of strength due to the lowering in the density, resulting in the instability of the quality of the molded product.